This invention relates to flow meters for measuring the rate of flow of a fluid media, either liquid or gaseous. More particularly, the invention relates to a flow meter having an output signal capable of being transmitted to a remote or proximate receiver for display and/or further manipulation.
This invention relates to flow meters in general but will be described with particular reference to variable area flow meters. A first type of variable area flow meter normally comprises a housing having an inlet port and an outlet port, a cylindrical core tube receiving flow into its interior from the input port of the housing and an output slot along the side of the core tube. A movable piston within the core tube responds to the fluid flowing through the core tube by opening the slot sufficiently to allow the flow demanded. An indicator attached to the movable piston is indexed against a scale showing the position of the piston and thereby the flow through the meter. Variable area flow meters are rugged, reliable, accurate and fluidtight. The construction of such flow meters and their theory of operation are described in U.S. Pats. Nos. 3,691,834; 4,361,051; and 4,489,614, all of which are incorporated hereinby reference.
A second type of variable area flow meter, generally known as a rotameter comprises an inlet port, a vertically disposed, upwardly expanding conical chamber and an outlet port. A piston disposed in the conical chamber forms a restriction in the cross-sectional area of the conical chamber. The piston rises or falls within the chamber, thus varying the area of the restriction, in response to changes in flow. An indicator attached to the piston is indexed against a scale and shows flow rate.
Prior art flow meters, including those described in the above-referenced U.S. patents, provide reliable, accurate readings of flow rate at the point at which a meter is disposed. Moreover, such prior art devices could be adapted to provide electrical signals generally indicative of flow rate. However, such electrical flow meters are expensive. Moreover, the means used to produce electrical signals, such as differential transformers, required that the overall flow meter be much larger than a non-electrical flow meter.
The present invention contemplates a flow meter providing electrical output usable by process control equipment and/or capable of operating a remote display which overcomes the above referred to problems and others and provides a compact, accurate flow meter which is simple to install and use and economical to manufacture.
In accordance with the present invention, there is provided a flow meter comprising a housing, a core tube, a piston slidably retained within the core tube which changes its position in accordance with flow through the core tube, a magnet fixed to the piston and a potentiometer comprised of two bars and a contact positioned such that the contact moves along the bars in lock step with the magnet thereby generating a signal indicative of magnet position and flow.
Further in accordance with the invention, the potentiometer provided is comprised of two parallel bars, one bar being a solid metallic bar and the other bar comprising a central core surrounded by a tightly helically wound fine wire.
Still further in accordance with the invention, the contact used in the potentiometer is a metallic ball electrically contacting both bars.
Yet further in accordance with the invention, the poteniometer bars are both circular in cross-section and have a ratio of diameters of 0.075 to 0.125 and the diameter of the ball is 2.08 times the diameter of the smaller bar.
Still further in accordance with the invention, the poteniometer comprised of the ball and two bars is enclosed in a transducer assembly having a transparent outwardly facing surface to which is fixed a scale whereby flow may be visually read at the location of the flow meter in addition to visually read in an electronic display signal or otherwise at the remote location.
Yet further in accordance with the invention, a transducer assembly is provided with mounting rings allowing the transducer to be mounted on the mechanical portions of a flow meter by simply sliding the transducer into place.
Still further in accordance with the invention electronic circuitry is provided processing the signal generated by the poteniometer. The potentiometer signal representative of magnet position is digitized. The digitized position signal is used to access an erasable programmable read only memory (EPROM) location containing a digital correction datum for that particular position. The digitized position figure and the digital correction datum are added to produce a digital flow signal for display. The digital correction figure is also converted to an analog correction signal and added to the potentiometer signal to create a corrected analog flow signal. An analog variable voltage, an analog variable current signal and a digital signal, all directly indicative of flow are thereby created. Additionally, digital integration of flow rates over time to provide total flow and/or other signal processing is also performed allowing display of such signals or the creation and delivery of such signals to a digital computer or other process control equipment for control of an overall process.
It is the primary object of the present invention to provide a reliable, accurate, economical and rugged flow meter having an output which is usable by process control equipment and easily carried to a remote location for further signal processing and/or display.
It is another object of the present invention to provide a flow meter having an output signal available at a remote location and also a local reading of flow at the location of the meter.
It is another object of the invention to provide a flow meter having electrical output signals usable by process control equipment and no electrical parts exposed to fluid being measured.
It is yet another object of the present invention to provide a flow meter having an electrical output and/or other easily transmittible output available at a remote location and a mechanically driven output signal, such as a ball and scale, available at the position of the flow meter even during periods of electrical failure or electronic malfunction.
It is yet another object of the present invention to provide a flow meter having electronic signal processing capabilities such that the flow meter may contribute data and/or signal processing capabilities to larger process control equipment.
It is another object of the invention to provide a transducer assembly which can be slipped over a mechanically complete flow meter and be immediately operable without the need to open the mechanical portions of the flow meter for adjustment or interconnection.
It is a further object of the invention to provide a flow meter having an electrical output, no dynamic seals and complete isolation between the fluid being measured and the meter's electrical parts.
It is still another object of the present invention to provide an electronic flow meter which is very precise and provides repeatable signals.
The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof.